Magnetic Tape Apparatus That Duplicates Data and Stores the Duplicated Data in Plural Magnetic Tape Drives

1. A magnetic tape apparatus comprising: a plurality of magnetic tape drives, and a control unit for reading and writing information from/in the magnetic tape drives by a command from a host computer, wherein said control unit includes: means for storing the same data in the plurality of magnetic tape drives while duplicating the data; means for, when the reading duplicated data from one magnetic tape drive is completed, performing positioning such that a read position of another magnetic tape drive in which the same data is stored is advanced by a length corresponding to an amount of data read from one magnetic tape drive; and means for continuing read of data from the other magnetic tape drive when data is unsuccessfully read from one magnetic tape drive; a master magnetic tape drive, a slave magnetic tape drive; a control unit for reading and writing information from/in the magnetic tape drives by a command from a host computer, wherein said control unit includes: means for storing the same data in the magnetic tape drives while duplicating the data; means for, when the reading duplicated data from the master magnetic tape drive is completed by one block, performing positioning such that a read position of the slave magnetic tape drive is advanced by one block; and means for continuing read of data from the slave magnetic tape drive when data is unsuccessfully read from the master magnetic tape drive; an operation state information storage area of the magnetic tape drives, and the control unit, wherein said control unit includes: means for, when a process to the magnetic tape drive cannot be executed, storing information representing that the magnetic tape drive is unusable in the operation state information storage area; means for reducing the magnetic tape drive in which the unusable information is stored to set the magnetic tape drive in a standby state; and operation state rewriting means for, when the control unit recognizes that a slave magnetic tape drive is in a standby state with reference to the operation state information storage area, reading data from the slave magnetic tape drive, when the data of the slave magnetic tape drive can be read, checking whether or not data in a data block is equal to data in a data block which is being read at the present on the master magnetic tape drive, and rewriting the operation state information of the slave magnetic tape drive into information representing that the data can be read and written when the data are equal to each other.

2. A magnetic tape apparatus according to claim 1 , comprising: data blocks in the magnetic tape drives, wherein the both data blocks include the same block identification information, the operation state rewriting means, when a data block of the slave magnetic tape drive in a standby state cannot be read, detects a readable data block subsequent to the data block, and, when a block identification number of the readable data block is larger than a data block identification number of the data block which is being read from the master magnetic tape drive, rewrites the operation state information of the slave magnetic tape drive into information representing an incorporation waiting state, and the control unit does not read data from a magnetic tape drive on which the operation state information is the incorporation waiting state.

3. A method for controlling an operation of a magnetic tape apparatus including a master magnetic tape drive, a slave magnetic tape drive, and a control unit for reading and writing information from/in the magnetic tape drives by a command from a host computer, the control unit including means for storing the same data in the magnetic tape drives + while duplicating the data, to read the duplicated data stored in the magnetic tape drives, comprising the steps of: A. the control unit, when the reading duplicated data from the master magnetic tape drive is completed by one block, performs positioning such that a read position of the slave magnetic tape drive is advanced by one block; B. the control unit continues read of data from the slave magnetic tape drive when data is unsuccessfully read from the master magnetic tape drive; C. storing information related to operation states of the magnetic tape drives; D. when a process to the magnetic tape drive cannot be executed, storing information representing that the magnetic tape drive is unusable in an operation state information storage area; E. reducing the magnetic tape drive in which the unusable information is stored to set the magnetic tape drive in a standby state; F. when it is recognized that the slave magnetic tape drive is in a standby state with reference to the operation state information storage area, reading data from the slave magnetic tape drive; G. when the data of the slave magnetic tape drive can be read, checking whether or not data in a data block read when the data can be read is equal to data in a data block which is being read at the present on the master magnetic tape drive; and H. rewriting the operation state information of the slave magnetic tape drive into information representing that the data can be read and written when the data are equal to each other.

4. The method of claim 3 , wherein said method further comprises: I. when a data block in the data blocks which is in the tape drives and including the same block identification information, of the slave magnetic tape drive in the standby state cannot be read, detecting a readable data block subsequent to the data block; and J. when a block identification number of the readable data block is larger than a data block identification number of the data block which is being read from the master magnetic tape drive, rewriting the operation state information of the slave magnetic tape drive into information representing an incorporation waiting state; and K. data is not read from the magnetic tape drive on which the operation state information is the incorporation waiting state.

5. A computer-readable storage medium recording thereon a program which causes a computer to perform the steps of A. the control unit, when the reading duplicated data from the master magnetic tape drive is completed by one block, performs positioning such that a read position of the slave magnetic tape drive is advanced by one block; and B. the control unit continues read of data from the slave magnetic tape drive when data is unsuccessfully read from the master magnetic tape drive; C. storing information related to operation states of the magnetic tape drives; D. when a process to the magnetic tape drive cannot be executed, storing information representing that the magnetic tape drive is unusable in the operation state information storage area; and E. reducing the magnetic tape drive in which the unusable information is stored to set the magnetic tape drive in a standby state; F. when it is recognized that the slave magnetic tape drive is in a standby state with reference to the operation state information storage area, reading data from the slave magnetic tape drive; G. when the data of the slave magnetic tape drive can be read, checking whether or not data in a data block read when the data can be read is equal to data in a data block which is being read at the present on the master magnetic tape drive; and H. rewriting the operation state information of the slave magnetic tape drive into information representing that the data can be read and written when the data are equal to each other.

6. A computer-readable storage medium recording thereon a program which causes a computer to perform said steps of A. the control unit, when the reading duplicated data from the master magnetic tape drive is completed by one block, performs positioning such that a read position of the slave magnetic tape drive is advanced by one block; B. the control unit continues read of data from the slave magnetic tape drive when data is unsuccessfully read from the master magnetic tape drive; C. storing information related to operation states of the magnetic tape drives; D. when a process to the magnetic tape drive cannot be executed, storing information representing that the magnetic tape drive is unusable in the operation state information storage area; E. reducing the magnetic tape drive in which the unusable information is stored to set the magnetic tape drive in a standby state; F. when it is recognized that the slave magnetic tape drive is in a standby state with reference to the operation state information storage area, reading data from the slave magnetic tape drive; G. when the data of the slave magnetic tape drive can be read, checking whether or not data in a data block read when the data can be read is equal to data in a data block which is being read at the present on the master magnetic tape drive; H. rewriting the operation state information of the slave magnetic tape drive into information representing that the data can be read and written when the data are equal to each other; I. when a data block in the data blocks which is in the tape drives and including the same block identification information, of the slave magnetic tape drive in the standby state cannot be read, detecting a readable data block subsequent to the data block; J. when a block identification number of the readable data block is larger than a data block identification number of the data block which is being read from the master magnetic tape drive, rewriting the operation state information of the slave magnetic tape drive into information representing an incorporation waiting state; and K. data is not read from the magnetic tape drive on which the operation state information is the incorporation waiting state.